[TowerTalk] Relay for sloper element

[Jim Thomson]

Date: Thu, 23 Nov 2017 12:17:33 -0500
From: "Gene Smar" <ersmar at verizon.net>
To: <towertalk at contesting.com>
Subject: [TowerTalk] Relay for sloper element


<    I want to be able to switch a piece of #14 house wire onto the far end
<of a sloper wire I have for 75 M phone so I can operate lower in the band.
I'm thinking of adding a relay in a weather-resistant box at the sloper's
end insulator and continue with the extension wire beyond that.  

     My question to this august group:  What relay (and supplier) would you
recommend for the job?  

     In the alternative, can you point me to a good source of info on
designing traps for said application?  The trap would not require any DC for
switching but might take more "cypherin' " to get working.  

     Many thanks and Happy Thanksgiving to all y'all.

73 de
Gene Smar  AD3F

##  Ok, this is a quarter wave sloper.   A trap wont work, since you just want to be able
to move the resonant freq down a bit.   The far end is sky high voltage,  esp with 1.5 kw,
so  dont add wire at the extreme end. 

##  Install a spst relay  or a DPST relay... with  contacts in parallel.  The DPST relay, with contacts
in parallel, will provide for doubling the RF current capacity and also provides for redundant contacts.  
Use a 12 vdc relay coil, then  feed it with 13.8 vdc  from the shack. 

##  A small  coil, like with  wound with a total of 4 foot of wire would shift the resonant freq down by 
250 khz.   All the relay does is, shorts the coil out.  A  3 inch diam coil  has a 12 inch circumference, 
so 4 turns would suffice.  Or use a smaller diam coil and a more turns.   Install the coil at the feedpoint,
next to the tower.  A  40 A  sealed spst  automotive type relay  would work, as will a lot of other relays. 
The peak V at the 50 ohm feedpoint is aprx   388 volts...assuming 1.5 kw into 50 ohms.  

##  another method is to use bigger gauge wire to begin with.   10 gauge wire is a LOT more broad banded 
vs  14 gauge... when using qtr wave slopers.    Im talking about the main sloper, not the coil.    14 gauge 
will work just fine for the small coil. 

##  either  a separate control cable for the 13.8 vdc.... or  a bias T will work.    I have used both schemes in the 
past.   If u just want to shift the res point from say  3850.... down to say 3600, the above coil + relay setup
will work just fine.  The default will be the lower freq, with  coil de-energized.   If u use a NC relay, then its
the other way around. 

Jim   VE7RF